Move single use, not explicitly tested helpers into the file that uses them.

lib/md048.js

@@ -2,10 +2,25 @@
 
 "use strict";
 
-const { addErrorDetailIf, fencedCodeBlockStyleFor } = require("../helpers");
+const { addErrorDetailIf } = require("../helpers");
 const { getDescendantsByType } = require("../helpers/micromark-helpers.cjs");
 const { filterByTypesCached } = require("./cache");
 
+/**
+ * Return the string representation of a fence markup character.
+ *
+ * @param {string} markup Fence string.
+ * @returns {"tilde" | "backtick"} String representation.
+ */
+function fencedCodeBlockStyleFor(markup) {
+  switch (markup[0]) {
+    case "~":
+      return "tilde";
+    default:
+      return "backtick";
+  }
+};
+
 // eslint-disable-next-line jsdoc/valid-types
 /** @type import("./markdownlint").Rule */
 module.exports = {